1. Field of the Invention
The present invention relates to a signal processing system in which data generated by a data input unit, such as a keyboard or a mouse, is transferred to a signal processing unit, including a personal computer, and processing according to the data is performed in the signal processing unit.
2. Description of the Related Art
As an input unit for inputting positional coordinate data which indicates the position of a cursor on the screen of a personal computer, a mouse or a trackball can be used which is provided with a ball and which changes the display position of the cursor according to the rotation direction and the amount of rotation of the ball.
FIG. 3 is a view illustrating the structure of a mechanical section of a mouse.
In this figure, a ball 1 is mounted rotatably about its center point. On the surface of the ball 1, rollers 3X and 3Y secured to rotatable shafts 2X and 2Y are pressed at two points through which the radii form 90 degrees, respectively. The direction indicated by arrow X is hereinafter called a +X direction (the reverse direction is called an -X direction) in the figure, and the direction indicated by arrow Y is hereinafter called a +Y direction (the reverse direction is called an -Y direction). At ends of the shafts 2X and 2Y, circular choppers 4X and 4Y are secured, respectively. At the peripheries of the choppers 4X and 4Y, a plurality of the same-size slits are disposed at an equal interval.
Photo-interrupters 5X and 5Y are mounted for the choppers 4X and 4Y, respectively. The photo-interrupters 5X and 5Y are provided with light-emitting devices (not shown) and light-receiving devices (not shown). The photo-interrupters 5X and 5Y are disposed against the chopper 4X and 4Y such that the peripheries of the choppers are disposed between the light-emitting devices and the light-receiving devices. The chopper 4X and the photo-interrupter 5X form an optical encoder 6X, and the chopper 4Y and the photo-interrupter 5Y form an optical encoder 6Y.
In this structure, when the ball 1 rotates, the shafts 2X and 2Y are rotated through the rollers 3X and 3Y, and the choppers 4X and 4Y are rotated accordingly. A power voltage V is applied to the photo-interrupters 5X and 5Y. The light-emitting devices are always emitting light. Therefore, when the choppers 4X and 4Y are rotated, blade-shaped portions between the slits formed at the peripheries of the choppers 4X and 4Y sequentially pass between the light-emitting devices and the light-receiving devices of the photo-interrupters 5X and 5Y. With this, light emitted from a light-emitting device to the corresponding light-receiving device is chopped and the levels of the signals P.sub.XA, P.sub.XB, P.sub.YA, and P.sub.YB output from the light-receiving devices are changed like pulses.
FIG. 4 is a block diagram of a circuit section of the mouse.
The circuit shown in the figure is provided for each of the two optical encoders 6X and 6Y. For simplicity, one of the two circuits is taken (that for the optical encoder 6X) and will be described. The configuration and the operation of the other circuit (that for the optical encoder 6Y) is the same as those of the circuit taken.
Light-emitting diodes 8A and 8B, for example, serve as the light-emitting devices provided for the photo-interrupter 5X. Phototransistors 9A and 9B, for example, serve as the light-receiving devices provided for the photo-interrupter 5X. In order to detect the rotation direction (along the X-axis) of the ball 1, the photo-interrupter 5X is provided with two pairs of light-emitting diodes and phototransistors as shown in FIG. 4. The output pulse P.sub.XA of the phototransistor 9A and the output pulse P.sub.XB of the phototransistor 9B have different phases in terms of the rising edge of a pulse according to the rotation direction of the chopper 4X (namely, the ball 1). In other words, when the ball 1 rotates in the +X direction, the output pulse P.sub.XA rises earlier than the output pulse P.sub.XB. When the ball 1 rotates in the -X direction, the output pulse P.sub.XB rises earlier than the output pulse P.sub.XA.
According to the phase relationship between the output pulse P.sub.XA and the output pulse P.sub.XB, a rotation-direction detector 10 detects the rotation direction of the chopper 4X. An up/down counter 9 counts the output pulses of the phototransistors. The up/down counter 9 counts in an ascending order or an descending order, depending on the rotation direction of the chopper 4X, detected by the rotation-direction detector 10. A controller 111 transfers the count N of the up/down counter 9 to the signal processing unit (not shown), such as a personal computer.
In the foregoing conventional signal processing system, when the ball 1 is rotated largely, the number of the output pulses of a light-receiving device (phototransistor) becomes large and the count of the pulses increases accordingly. Therefore, the amount of data to be transferred to the signal processing unit becomes large.